This invention relates to control circuitry for controlling the video picture displayed by a television receiver and, more particularly, to contrast and color level control circuitry capable of adjusting the contrast and color level of the video picture in response to remotely transmitted command signals.
In a typical color television receiver which includes a luminance channel and a chrominance channel, the contrast of the video picture displayed by the television receiver is controlled by selectively adjusting the gain of the luminance channel in accordance with a viewer's preference. If the gain of the luminance channel is, for example, increased, the luminance signal which is processed by that channel is, correspondingly, increased. For a monochrome, or black-and-white video picture, the contrast likewise is increased. However, for a color video picture, if the chrominance signal is not changed as the luminance signal changes, then the chrominance-to-luminance signal ratio, or C/Y, will not remain constant. That is, and in accordance with the foregoing example, if the luminance signal is increased without a concommitent increase in the chrominance signal, then the chrominance-to-luminance signal ratio C/Y decreases. As a consequence thereof, the resultant increase in contrast has the visual effect of reducing the overall color level of the video picture.
Accordingly, to avoid the aforenoted defect, it is not unusual to provide some intercoupling between the contrast control circuit and the color level control circuit in a color television receiver. That is, provision is made to proportionally change the chrominance signal level when the luminance signal level is changed, thereby adjusting the color level with adjustments in contrast so as to maintain a constant chrominance-to-luminance signal ratio C/Y.
The gain of the luminance signal in a color television receiver readily is controlled by using a gain-controlled video amplifier. Similarly, the gain of the chrominance signal, that is, the color level of the video picture, readily is controlled by using a gain-controlled chrominance amplifier. Hence, contrast adjustments are effected by selectively adjusting the gain-controlling bias voltage applied to the video amplifier. In like manner, adjustments in the color level are made by selectively adjusting the gain-controlling bias voltage which is applied to the chrominance amplifier. Typically, these bias voltages are derived from adjustable resistors, such as potentiometers. A reference voltage is applied across a contrast adjustment potentiometer such that the contrast adjustment bias voltage is a function of the position of the tap of this potentiometer. Similarly, a voltage is applied across the color level adjustment potentiometer, and the color level bias voltage is determined by the position of the tap of this potentiometer. In order to insure that a change in the contrast adjustment bias voltage is accompanied by a proportional change in the color level adjustment bias voltage so that the chrominance-to-luminance signal ratio C/Y remains constant, the voltage which is applied across the color level adjustment potentiometer is derived from the output of the contrast adjustment potentiometer. Hence, an adjustment in the contrast of the displayed video picture is accompanied by a change in the voltage applied across the chrominance adjustment potentiometer, thereby producing a proportional change in the color level adjustment bias voltage which is applied to the chrominance amplifier. Therefore, a corresponding change in the color level is obtained, while maintaining a substantially constant C/Y ratio.
While the foregoing contrast and color level control circuitry operates satisfactorily in response to manual adjustments to the respective potentiometers, it generally is not susceptible of being remotely controlled. In a television receiver adapter for remote control over various functions, ultrasonic signals or infrared light signals are used to control particular functions from a remote location. For example, a viewer is provided with a transmitter, and the television receiver is provided with a compatible receiving device. Various command signals, such as power on/off, channel selection, and the like modulate or encode an ultrasonic wave or an infrared light wave in response to the viewer's selection. The compatible receiving device at the television receiver receives and demodulates the modulated ultrasonic wave or infrared light wave so as to reproduce the particular commond signal which, in turn, controls the appropriate on/off or channel selection function, or the like. With this type of remote-control trasmitting/receiving apparatus, it is quite difficult to obtain an economical technique for controlling the above-mentioned contrast adjustment and color level adjustment potentiometers. This is because such potentiometers would have to be adjusted by selectively energizable motors. The use of such motors and suitable control circuitry therefor is very expensive.
Although it may present no substantial difficulty in providing a remote control operation over contrast adjustment, this generally will be achieved without a concommitent adjustment in the color level of the displayed video picture. This is because remote control over contrast would be accomplished without the use of potentiometers, and especially intercoupled contrast adjustment and color level adjustment potentiometers. Hence, the contrast and color level control circuitry heretofore known to the prior art suffers from the disadvantage that proper contrast and color level adjustments cannot be made by remote control. At best, separate adjustments can be achieved independently of each other, thereby changing the desirably constant chrominance-to-luminance ratio C/Y when contrast is adjusted.